Propylene butene copolymer

ABSTRACT

The invention provides a multimodal propylene butene random copolymer having a melt flow rate (MFR 2 ) of 1.0 to 20.0 g/10 min and a butene content of 5.0 to 20.0 wt %, wherein said copolymer is prepared using a single site catalyst and wherein said copolymer comprises: (i) 30 to 70 wt % of a propylene butene copolymer (A) having an MFR 2  of 0.5 to 20.0 g/10 min and a butene content of 2.0 to 10.0 wt %; and (ii) 70 to 30 wt % of a propylene butene copolymer (B) having an MFR 2  of 0.5 to 20.0 g/10 min and a butene content of 4.0 to 20.0 wt %; wherein copolymers (A) and (B) are different.

FIELD OF THE INVENTION

This invention relates to a propylene butene random copolymer, inparticular to a multimodal propylene butene random copolymer preparedusing a single site catalyst. The invention further relates to a processfor preparing said random copolymer and to articles, such as films,comprising said random copolymer.

BACKGROUND

Packaging films based on polyolefins are well known in the literature,as these can generally be easily processed, are light in weight, stableto environmental conditions and are capable of being tailored toparticular applications to meet the varying demands of the packagingfield. Food packaging in particular places several high demands on thematerial used. First, the packaging must be sufficiently tight in orderto sufficiently protect the packaged or sealed-material, and to make thehandling of the sealed products, in particular during transport,sufficiently safe. Thus, good sealing behaviour is desired. Ideally, thefilms are heat-sealable at as a low temperature as possible to minimiseenergy input during the sealing process.

Another important consideration is mechanical properties. Polymers withhigher stiffness may allow for the use of lower film thicknesses,leading to both material and energy savings. Good impact behaviour isalso essential so the contents of the packaging remain safely contained,even if dropped.

Sterilisation behaviour must also be considered since materials used infood packaging application are now typically subjected to sterilisationbefore use. The most common sterilisation procedures are the use of heat(steam), radiation (beta radiation, electrons, or gamma radiation) orchemicals (usually ethylene oxide). Steam sterilisation is usuallycarried out in a temperature range of about 120 to 130° C. Thus, thematerial should have a sufficient thermal stability, like a meltingtemperature higher than the usual steam sterilisation temperature ofabout 120 to 130° C.

Of course, treatment of a polymer under the sterilisation conditionsoutlined above can impair its final properties, especially the opticalproperties such as transparency. Thus, ideally, excellent sterilisationbehaviour in terms of retention of low haze level after sterilisation isdesirable.

Polypropylene random copolymers are widely used in such packagingapplications due to their good balance of properties. Typically theseare copolymers of propylene and ethylene. In order to fulfil thedifferent requirements of the packaging, however, and provide thenecessary balance of properties, these copolymers have normally beenapplied as multilayer structures. For example, a low Tm (meltingtemperature) propylene ethylene copolymer layer, which provides the bestsealing properties, is combined with a higher Tm propylene ethylenecopolymer, which offers good stiffness. These types of structures aredescribed in, for example, EP 2965908. The use of multilayer structureshas a number of drawbacks, however. Principally these include complexityin the production of the materials and recycling. There is a driveacross all areas of industry, particularly in the field of plastics, toincrease recyclability of the materials used. Multilayer structurespresent a substantial challenge for reuse.

Propylene butene copolymers are also known in film applications (e.g. asdescribed in EP 3257878), however the majority of these grades are madeusing Ziegler-Natta (ZN) catalysts. Disadvantages associated with theuse of ZN catalysts are that they tend to produce a lot of oligomers andhigh comonomer contents are needed in order to achieve desirable lowmelting temperatures.

It is thus an object of the present invention to provide a new polymerwhich can overcome at least some of the problems associated with thosecurrently employed. A polymer which offers an attractive balance ofproperties for application in the food packaging field is looked-for. Inparticular, a polymer which can be employed as a single layer materialis desirable. Preferably, more than one of these factors is achieved.

SUMMARY

Thus, in a first aspect, the invention provides a multimodal propylenebutene random copolymer having a melt flow rate (MFR₂) of 1.0 to 20.0g/10 min and a butene content of 5.0 to 20.0 wt %, wherein saidcopolymer is prepared using a single site catalyst and wherein saidcopolymer comprises:

-   -   (i) 30 to 70 wt % of a propylene butene copolymer (A) having an        MFR₂ of 0.5 to 20.0 g/10 min and a butene content of 2.0 to 10.0        wt %; and    -   (ii) 70 to 30 wt % of a propylene butene copolymer (B) having an        MFR₂ of 0.5 to 20.0 g/10 min and a butene content of 4.0 to 20.0        wt %;    -   wherein copolymers (A) and (B) are different.

In a second aspect, the invention provides the process for thepreparation of a multimodal propylene butene random copolymer ashereinbefore defined, said process comprising:

-   -   (i) polymerising propylene and butene in a first polymerisation        stage in the presence of a single site catalyst to prepare a        first propylene butene copolymer having a MFR₂ from 0.5 to 20.0        g/10 min and a butene content of 2.0 to 10.0 wt %;    -   (ii) polymerising propylene and butene in a second        polymerisation stage in the presence of said catalyst and said        first propylene butene copolymer to prepare said multimodal        propylene butene copolymer.

In a third aspect, the invention provides an article, such as a film,comprising a multimodal propylene butene copolymer as hereinbeforedefined.

In a final aspect, the invention provides the use of a multimodalpropylene butene random copolymer as defined herein for the manufactureof an article, preferably a film.

DETAILED DESCRIPTION Definitions

By “random” copolymer is meant a copolymer in which the comonomer unitsare randomly distributed within the copolymer. Specifically in thecontext of the present invention, the propylene butene random copolymeris thus a polymer in which the butene comonomer units are randomlydistributed within the copolymer.

Multimodal Propylene Butene Random Copolymer

It has been found that the multimodal propylene butene random copolymeraccording to the invention provides a new material suitable forpackaging applications, in particular as a film, which combines verygood mechanical properties e.g. in terms of stiffness (measured bytensile modulus), with attractive sealing properties (e.g. in terms of alow sealing temperature). In particular, by tuning the comonomerdistribution between the two copolymer fractions of the multimodalcopolymer, it is possible to access a broader property range in terms ofmechanical, sealing and optical properties than has previously beenpossible. The copolymer also possesses good sterilisation behaviourwhich is of particular importance in the food packaging industry.Sterilisation behaviour is typically measured via changes in properties(e.g. mechanics (toughness) or optics) after the sterilisation processIn the present invention, a comparison of haze before and aftersterilisation is performed, the less the negative change, the better thesterilisation.

The polymer of the invention is a multimodal polypropylene and is apropylene copolymer. By propylene copolymer is meant a polymer themajority by weight of which derives from propylene monomer units (i.e.at least 50 wt % propylene relative to the total weight of thecopolymer). The comonomer is butene. The butene content in multimodalcopolymer is in the range 5.0 to 20.0 wt % relative to the total weightof the copolymer, preferably 5.5 to 18.0 wt %, more preferably 6.0 to16.0 wt %, more preferably 6.5 to 14.0 wt %.

Whilst it is within the ambit of the invention for the multimodalpropylene butene random copolymer to comprise other copolymerisablemonomers, it is preferable that propylene and butene are the onlymonomers present, i.e. butene is the only comonomer. It is especiallypreferred if the multimodal propylene butene copolymer is substantiallyfree of ethylene, e.g. comprises less than 0.1 wt % ethylene, preferablyless than 0.01 wt % ethylene, more preferably less than 0.001 wt %.

If present, other copolymerisable monomers may be ethylene or C5-12,especially C5-10, alpha olefin comonomers, particularly singly ormultiply ethylenically unsaturated comonomers, in particular C5-10-alphaolefins such as hex-1-ene, oct-1-ene, and 4-methyl-pent-1-ene. The useof 1-hexene and 1-octene is particularly preferred.

The polypropylene of the invention is multimodal. Usually, apolypropylene comprising at least two polypropylene fractions, whichhave been produced under different polymerisation conditions resultingin different (weight average) molecular weights and molecular weightdistributions for the fractions or different comonomer distributions, isreferred to as “multimodal”. Accordingly, in this sense the polymers ofthe invention are multimodal polypropylene. The prefix “multi” relatesto the number of different polymer fractions the polymer is consistingof. Preferably, the polypropylene is bimodal, i.e. consisting of twopolypropylene fractions (A) and (B).

The multimodal propylene butene random copolymer of the invention has amelt flow rate (MFR₂) of 1.0 to 20.0 g/10 min. Typically, the multimodalpropylene butene random copolymer has an MFR₂ of 18.0 g/10 min or less,preferably 16.0 g/10 min or less, more preferably 12.0 g/10 min or less,such as 10.0 g/10 min or less. The polymer preferably has a minimum MFR₂of 1.5 g/10 min, such as greater than 2.5 g/10 min, preferably at least3.5 g/10 min, ideally at least 4.0 g/10 min, especially 5.0 g/10 min ormore. Thus, particularly suitable values of MFR₂ are from 4.0 to 12.0g/10 min, such as 5.0 to 10.0 g/10 min.

The density of the polypropylene may typically be in the range 890 to907 kg/m³, ideally 900 to 905 kg/m³.

Preferably, the multimodal propylene butene copolymer has a flexuralmodulus of at least 750 MPa, more preferably at least 800 MPa, such asat least 830 MPa. Typically, the copolymer has a flexural modulus ofless than 1600 MPa, such as less than 1400 MPa.

The polypropylene polymer preferably has a molecular weight distributionMw/Mn, being the ratio of the weight average molecular weight Mw and thenumber average molecular weight Mn, of less than 4.5, such as 2.0 to4.0, e.g. 3.0.

Generally, the polypropylene polymer has a xylene soluble content (XCS)of less than 10.0 wt %, preferably less than 8.0 wt %, more preferablyless than 6.0 wt %, such as less than 5.0 wt %. A typical lower limitfor XCS may be 0.1 wt % or 0.5 wt %. The xylene soluble fraction isdetermined according to ISO 16152 at 25° C.

As noted above, the polymers of the invention preferably comprise atleast two polypropylene fractions (A) and (B). In one particularlypreferably embodiment, the multimodal polypropylene consists offractions (A) and (B). The weight ratio of fraction (A) to fraction (B)in the multimodal polypropylene is in the range 30:70 to 70:30, morepreferably 35:65 to 65:35, most preferably 40:60 to 60:40. In someembodiments the ratio may be 45 to 55 wt % of fraction (A) and 55 to 45wt % fraction (B), such as 50 wt % of fraction (A) and 50 wt % fraction(B).

It is a requirement of the invention that polymer fractions (A) and (B)are different.

(i) Propylene Butene Copolymer (A)

Fraction (A) is a propylene butene copolymer component. Typically,fraction (A) consists of a single propylene butene copolymer. Bypropylene copolymer is meant a polymer the majority by weight of whichderives from propylene monomer units (i.e. at least 50 wt % propylenerelative to the total weight of the copolymer). The comonomer is butene.The butene content in copolymer (A) is in the range 2.0 to 10.0 wt %relative to the total weight of the copolymer, preferably 3.0 to 9.0 wt%, more preferably 4.0 to 8.0 wt %.

Whilst it is within the ambit of the invention for the propylene butenecopolymer (A) to comprise other copolymerisable monomers, it ispreferable that propylene and butene are the only monomers present, i.e.butene is the only comonomer. It is especially preferred if copolymer(A) is substantially free of ethylene, e.g. comprises less than 0.1 wt %ethylene, preferably less than 0.01 wt % ethylene, more preferably lessthan 0.001 wt %.

If present, other copolymerisable monomers may be ethylene or C5-12,especially C5-10, alpha olefin comonomers, particularly singly ormultiply ethylenically unsaturated comonomers, in particular C5-10-alphaolefins such as hex-1-ene, oct-1-ene, and 4-methyl-pent-1-ene. The useof 1-hexene and 1-octene is particularly preferred.

The propylene butene copolymer (A) of the invention has a melt flow rate(MFR₂) of 0.5 to 20.0 g/10 min. Typically, the propylene butenecopolymer (A) has an MFR₂ of 15.0 g/10 min or less, preferably 12.0 g/10min or less, preferably 10.0 g/10 min or less, such as 8.0 g/10 min orless. The polymer preferably has a minimum MFR₂ of 1.0 g/10 min, such asgreater than 1.5 g/10 min, preferably at least 2.0 g/10 min. Thus,particularly suitable values of MFR₂ are from 1.0 to 10.0 g/10 min, suchas 2.0 to 8.0 g/10 min.

The propylene butene copolymer fraction (A) is present in an amount of30 to 70 wt %, preferably 35 to 65 wt %, more preferably 40 to 60 wt %,such as 45 to 55 wt %, e.g. 50 wt %.

(ii) Propylene Butene Copolymer (B)

Fraction (B) is a propylene butene copolymer component. Typically,fraction (B) consists of a single propylene butene copolymer. Bypropylene copolymer is meant a polymer the majority by weight of whichderives from propylene monomer units (i.e. at least 50 wt % propylenerelative to the total weight of the copolymer). The comonomer is butene.The butene content in copolymer (B) is in the range 4.0 to 20.0 wt %relative to the total weight of the copolymer, preferably 5.0 to 18.0 wt%, more preferably 6.0 to 16.0 wt %.

Whilst it is within the ambit of the invention for the propylene butenecopolymer (B) to comprise other copolymerisable monomers, it ispreferable that propylene and butene are the only monomers present, i.e.butene is the only comonomer. It is especially preferred if copolymer(B) is substantially free of ethylene, e.g. comprises less than 0.1 wt %ethylene, preferably less than 0.01 wt % ethylene, more preferably lessthan 0.001 wt %.

If present, other copolymerisable monomers may be ethylene or C5-12,especially C5-10, alpha olefin comonomers, particularly singly ormultiply ethylenically unsaturated comonomers, in particular C5-10-alphaolefins such as hex-1-ene, oct-1-ene, and 4-methyl-pent-1-ene. The useof 1-hexene and 1-octene is particularly preferred.

The propylene butene copolymer (B) of the invention has a melt flow rate(MFR₂) of 0.5 to 20.0 g/10 min. Typically, the propylene butenecopolymer (B) has an MFR₂ of 15.0 g/10 min or less, preferably 12.0 g/10min or less, preferably 10.0 g/10 min or less, such as 8.0 g/10 min orless. The polymer preferably has a minimum MFR₂ of 1.0 g/10 min, such asgreater than 1.5 g/10 min, preferably at least 2.0 g/10 min. Thus,particularly suitable values of MFR₂ are from 1.0 to 10.0 g/10 min, suchas 2.0 to 8.0 g/10 min.

The propylene butene copolymer fraction (B) is present in an amount of70 to 30 wt %, preferably 65 to 35 wt %, more preferably 60 to 40 wt %,such as 55 to 45 wt %, e.g. 50 wt %.

Preparation of Multimodal Propylene Butene Random Copolymer

The multimodal propylene butene random copolymer of the invention may beprepared by any known process in the art, such as by blending the twofractions (A) and (B). However, preferably, the multimodal copolymer isproduced in a multistage process wherein fractions (A) and (B) areproduced in subsequent stages. The properties of the fractions producedin a higher stage of the multistage process may be calculated asfollows.

The MFR of the second fraction (B), produced in the second reactor isdetermined according to

${\log\left( {{MFR}(B)} \right)} = \frac{{\log\left( {{MFR}\left( {{PP} - {Copo}} \right)} \right)} - {{w(A)}*{\log\left( {{MFR}(A)} \right)}}}{w(B)}$

whereinMFR (PP-Copo) denominates the MFR propylene butene copolymerw(A) and w(B) denominate the weight fractions of the first polypropylenefraction and second polypropylene fraction respectivelyMFR(A) denominates the MFR of the first polypropylene fraction (A)produced in the first reactor.

Thus, although not directly measurable on the multistage processproducts, the properties of the fractions produced in higher stages ofsuch a multistage processes may be determined by applying the abovemethod.

Multimodal propylene copolymers produced in a multistage process arealso designated as “in-situ” blends. The resulting end product consistsof an intimate mixture of the polymers from the two or more reactors.These two polymers may have different molecular-weight-distributioncurves, and/or they may differ in terms of comonomer content or type.The end product thus contains a mixture or two or more polymers withdiffering properties, i.e. it is a multimodal polymer mixture

In a particularly, preferred embodiment, the multimodal propylene butenerandom copolymer is prepared by a process comprising:

-   -   (i) polymerising propylene and butene in a first polymerisation        stage in the presence of a single site catalyst to prepare a        first propylene butene copolymer having a MFR₂ from 0.5 to 20.0        g/10 min and a butene content of 2.0 to 10.0 wt %;    -   (ii) polymerising propylene and butene in a second        polymerisation stage in the presence of said catalyst and said        first propylene butene copolymer to prepare said multimodal        propylene butene random copolymer.

The first polymerisation stage is preferably a slurry polymerisationstep. The slurry polymerisation usually takes place in an inert diluent,typically a hydrocarbon diluent such as methane, ethane, propane,n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or theirmixtures. Preferably the diluent is a low-boiling hydrocarbon havingfrom 1 to 4 carbon atoms or a mixture of such hydrocarbons. Anespecially preferred diluent is propane, possibly containing minoramount of methane, ethane and/or butane.

The temperature in the first polymerisation stages is typically from 60to 100° C., preferably from 70 to 90° C. An excessively high temperatureshould be avoided to prevent partial dissolution of the polymer into thediluent and the fouling of the reactor. The pressure is from 1 to 150bar, preferably from 40 to 80 bar.

The slurry polymerisation may be conducted in any known reactor used forslurry polymerisation. Such reactors include a continuous stirred tankreactor and a loop reactor. It is especially preferred to conduct thepolymerisation in a loop reactor. In such reactors the slurry iscirculated with a high velocity along a closed pipe by using acirculation pump. Loop reactors are generally known in the art andexamples are given, for instance, in U.S. Pat. Nos. 4,582,816,3,405,109, 3,324,093, EP-A-479186 and U.S. Pat. No. 5,391,654. It isthus preferred to conduct the first polymerisation stage as a slurrypolymerisation in a loop reactor.

The slurry may be withdrawn from the reactor either continuously orintermittently. A preferred way of intermittent withdrawal is the use ofsettling legs where slurry is allowed to concentrate before withdrawinga batch of the concentrated slurry from the reactor. The use of settlinglegs is disclosed, among others, in U.S. Pat. Nos. 3,374,211, 3,242,150and EP-A-1310295. Continuous withdrawal is disclosed, among others, inEP-A-891990, EP-A-1415999, EP-A-1591460 and WO-A-2007/025640. Thecontinuous withdrawal is advantageously combined with a suitableconcentration method, as disclosed in EP-A-1310295 and EP-A-1591460. Itis preferred to withdraw the slurry from the first polymerisation stagecontinuously.

Hydrogen is typically introduced into the first polymerisation stage forcontrolling the MFR₂ of the propylene butene copolymer (A). The amountof hydrogen needed to reach the desired MFR depends on the catalyst usedand the polymerisation conditions, as will be appreciated by the skilledworker.

The average residence time in the first polymerisation stage istypically from 20 to 120 minutes, preferably from 30 to 80 minutes. Asit is well known in the art the average residence time τ can becalculated from Equation 1 below:

$\begin{matrix}{{{Residence}\mspace{14mu}{Time}}{\tau = \frac{V_{R}}{Q_{o}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Where V_(R) is the volume of the reaction space (in case of a loopreactor, the volume of the reactor, in case of the fluidized bedreactor, the volume of the fluidized bed) and Q_(o) is the volumetricflow rate of the product stream (including the polymer product and thefluid reaction mixture).

The production rate is suitably controlled with the catalyst feed rate.It is also possible to influence the production rate by suitableselection of the monomer concentration. The desired monomerconcentration can then be achieved by suitably adjusting the propylenefeed rate.

The second polymerisation stage is preferably a gas phase polymerisationstep, i.e. carried out in a gas-phase reactor. Any suitable gas phasereactor known in the art may be used, such as a fluidised bed gas phasereactor.

For gas phase reactors, the reaction temperature used will generally bein the range 60 to 115° C. (e.g. 70 to 110° C.), the reactor pressurewill generally be in the range 10 to 25 bar, and the residence time willgenerally be 1 to 8 hours. The gas used will commonly be a non-reactivegas such as nitrogen or low boiling point hydrocarbons such as propanetogether with monomer (e.g. ethylene).

A chain transfer agent (e.g. hydrogen) is typically added to the secondpolymerisation stage.

The split between the first and second polymerisation stages may be inthe range 30:70 to 70:30, preferably 40:60 to 60:40, such as 45:55 to55:45, for example 50:50.

A preferred multistage process is the above-identified slurry-gas phaseprocess, such as developed by Borealis and known as the Borstar®technology. In this respect, reference is made to the EP applications EP0887379 A1 and EP 0517868 A1.

The polymerisation steps discussed above may be preceded by aprepolymerisation step. The purpose of the prepolymerisation is topolymerise a small amount of polymer onto the catalyst at a lowtemperature and/or a low monomer concentration. By prepolymerisation itis possible to improve the performance of the catalyst in slurry and/ormodify the properties of the final polymer. The prepolymerisation stepis typically conducted in slurry.

Thus, the prepolymerisation step may be conducted in a loop reactor. Theprepolymeriszation is then preferably conducted in an inert diluent,typically a hydrocarbon diluent such as methane, ethane, propane,n-butane, isobutane, pentanes, hexanes, heptanes, octanes etc., or theirmixtures. Preferably the diluent is a low-boiling hydrocarbon havingfrom 1 to 4 carbon atoms or a mixture of such hydrocarbons.

The temperature in the prepolymerisation step is typically from 0 to 90°C., preferably from 20 to 80° C. and more preferably from 55 to 75° C.

The pressure is not critical and is typically from 1 to 150 bar,preferably from 40 to 80 bar.

The amount of monomer is typically such that from 0.1 to 1000 grams ofmonomer per one gram of solid catalyst component is polymerised in theprepolymerisation step. As the person skilled in the art knows, thecatalyst particles recovered from a continuous prepolymerisation reactordo not all contain the same amount of prepolymer. Instead, each particlehas its own characteristic amount which depends on the residence time ofthat particle in the prepolymerisation reactor. As some particles remainin the reactor for a relatively long time and some for a relativelyshort time, then also the amount of prepolymer on different particles isdifferent and some individual particles may contain an amount ofprepolymer which is outside the above limits. However, the averageamount of prepolymer on the catalyst typically is within the limitsspecified above.

The molecular weight of the prepolymer may be controlled by hydrogen asit is known in the art. Further, antistatic additives may be used toprevent the particles from adhering to each other or the walls of thereactor, as disclosed in WO-A-96/19503 and WO-A-96/32420.

The catalyst components are preferably all introduced to theprepolymerisation step when a prepolymerisation step is present.However, where the solid catalyst component and the cocatalyst can befed separately it is possible that only a part of the cocatalyst isintroduced into the prepolymerisation stage and the remaining part intosubsequent polymerisation stages. Also in such cases it is necessary tointroduce so much cocatalyst into the prepolymerisation stage that asufficient polymerisation reaction is obtained therein.

It is understood within the scope of the invention, that the amount ofpolymer produced in the prepolymerisation typically lies within 1.0-5.0wt % in respect to the final multimodal propylene butene copolymer.

The multimodal propylene butene copolymer is prepared in the presence ofa single site catalyst (which term encompasses a metallocene and anon-metallocene catalyst). These terms have a well-known meaning. Mostpreferably, the catalyst is a metallocene

Any metallocene catalyst capable of catalysing the formation of anolefinic polymer can be used. A suitable metallocene catalyst comprisesa metallocene/activator reaction product impregnated in a porous supportat maximum internal pore volume. The catalyst complex comprises a ligandwhich is typically bridged, and a transition metal of group IVa to VIa,and an organoaluminium compound. The catalytic metal compound istypically a metal halide.

Suitable metallocene compounds are those which have a formula(Cp)_(m)R_(n) MR′_(o) X_(p), where Cp is an unsubstituted or substitutedand/or fused homo or heterocyclopentadienyl, R is a group having 1-4atoms and bridging two Cp rings, M is a transition metal of group 4, 5or 6 in the Periodic Table of Elements (IUPAC, 1985), R′ is C₁-C₂hydrocarbyl or hydrocarboxy group and X is a halogen atom, wherein m is1-3, n is 0 or 1, o is 0-3 and p is 0-3 and sum n+o+p corresponds theoxidation state of the transition metal M. The transition metal M ispreferably zirconium, hafnium or titanium, most preferably zirconium.

Examples of suitable metallocene compounds include those of formula (I)or (II):

wherein each X is a sigma ligand, preferably each X is independently ahydrogen atom, a halogen atom, C₁₋₆-alkoxy group, C₁₋₆-alkyl, phenyl orbenzyl group;

R′ is independently a C₁₋₆ alkyl or C₃₋₁₀ cycloalkyl;

R¹ is independently C₃₋₈ alkyl;

R⁶ is hydrogen or a C₃₋₈ alkyl group;

R^(6′) is a C₃₋₈ alkyl group or C₆₋₁₀ aryl group, preferably a tertiaryC₄₋₈ alkyl group;

R^(3′) is a C₁₋₆ alkyl group, or C₆₋₁₀ aryl group optionally substitutedby one or more halo groups; and

n is independently 0, 1 or 2.

Particular metallocene compounds include:

Alternatively, the metallocene compound may be selected from:

rac-anti-dimethylsilanediyl[2-methyl-4,7-bis-(3′,5′-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl][2-methyl-4-(3′,5′-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl]zirconium dichloride

or

anti-dimethylsilanediyl[2-methyl-4-(3,5-dimethylphenyl)-5-methoxy-6-tert-butylinden-1-yl][2-methyl-4-(3,5-dimethylphenyl)-1,5,6,7-tetrahydro-s-indacen-1-yl]zirconiumdichloride

Most preferablyrac-anti-Me₂Si(2-Me-4-(p-tBuPh)-Ind)(2-Me-4-Ph-5-OMe-6-tBu-Ind)ZrCl₂ isused.

Such metallocene catalysts are frequently used with catalyst activatorsor co-catalysts, e.g. alumoxanes such as methylaluminoxane, which arewidely described in the literature.

The metallocene catalyst may be supported as is well known in the art.Any suitable support or carrier material can be used, which may be anyporous, substantially inert support, such as an inorganic oxide or salt.In practice the support used is preferably a fine-grained inorganicoxide such as an inorganic oxide of an element of Group 2, 13 or 14 inthe Periodic Table of Elements (IUPAC, 1985), most preferably silica,alumina or a mixture or derivative of these. Other inorganic oxideswhich can be used either alone or together with silica, alumina orsilica-alumina, are magnesium oxide, titanium dioxide, zirconium oxide,aluminum phosphate etc.

Alternatively, the catalyst may be used in non-supported form or insolid form.

Non-supported catalyst systems, suitable for the present invention canbe prepared in solution, for example in an aromatic solvent liketoluene, by contacting the metallocene (as a solid or as a solution)with the cocatalyst(s), for example methylaluminoxane and/or a borane ora borate salt previously in an aromatic solvent, or can be prepared bysequentially adding the dissolved catalyst components to thepolymerisation medium.

The catalyst system of the invention in solid form, preferably in solidparticulate form is generally free from an external carrier, howeverstill being in solid form. By free from an external carrier is meantthat the catalyst does not contain an external support, such as aninorganic support, for example, silica or alumina, or an organicpolymeric support material.

In order to provide the catalyst system of the invention in solid formbut without using an external carrier, it is preferred if aliquid/liquid emulsion system is used. The process involves formingdispersing catalyst components (i) (the complex) and (ii)+optionally(iii) the cocatalysts) in a solvent, and solidifying said disperseddroplets to form solid particles. In particular, the method involvespreparing a solution of the catalyst components; dispersing saidsolution in an solvent to form an emulsion in which said one or morecatalyst components are present in the droplets of the dispersed phase;immobilising the catalyst components in the dispersed droplets, in theabsence of an external particulate porous support, to form solidparticles comprising the said catalyst, and optionally recovering saidparticles. This process enables the manufacture of active catalystparticles with improved morphology, e.g. with a predetermined particlesize, spherical shape, compact structure, excellent surface propertiesand without using any added external porous support material, such as aninorganic oxide, e.g. silica. The catalyst particles can have a smoothsurface, they may be compact in nature and catalyst active componentscan be distributed uniformly thorough the catalyst particles. Fulldisclosure of the necessary process steps can be found in, for example,WO03/051934.

All or part of the preparation steps can be done in a continuous manner.Reference is made to WO2006/069733 describing principles of such acontinuous or semicontinuous preparation methods of the solid catalysttypes, prepared via emulsion/solidification method. The formed catalystpreferably has good stability/kinetics in terms of longevity ofreaction, high activity and the catalysts enable low ash contents.

The use of the heterogeneous, non-supported catalysts, (i.e.“self-supported” catalysts) might have, as a drawback, a tendency todissolve to some extent in the polymerisation media, i.e. some activecatalyst components might leach out of the catalyst particles duringslurry polymerisation, whereby the original good morphology of thecatalyst might be lost. These leached catalyst components are veryactive possibly causing problems during polymerisation. Therefore, theamount of leached components should be minimized, i.e. all catalystcomponents should be kept in heterogeneous form.

Furthermore, the self-supported catalysts generate, due to the highamount of catalytically active species in the catalyst system, hightemperatures at the beginning of the polymerisation which may causemelting of the product material. Both effects, i.e. the partialdissolving of the catalyst system and the heat generation, might causefouling, sheeting and deterioration of the polymer material morphology.

In order to minimise the possible problems associated with high activityor leaching, it is preferred to “prepolymerise” the catalyst beforeusing it in polymerisation process. It has to be noted thatprepolymerisation in this regard is part of the catalyst preparationprocess, being a step carried out after a solid catalyst is formed. Thiscatalyst prepolymerisation step is not part of the actual polymerisationconfiguration, which might comprise a conventional processprepolymerisation step as well. After the catalyst prepolymerisationstep, a solid catalyst is obtained and used in polymerisation.

Catalyst “prepolymerisation” takes place following the solidificationstep of the liquid-liquid emulsion process hereinbefore described.Prepolymerisation may take place by known methods described in the art,such as that described in WO 2010/052263, WO 2010/052260 or WO2010/052264. Use of the catalyst prepolymerisation step offers theadvantage of minimising leaching of catalyst components and thus localoverheating.

The solvent employed in the processes of the invention may be anysolvent suitable for use in olefin polymerisation and is typically amixture of hydrocarbons. Such solvents are well known in the art.Examples of solvents include hexane, cyclohexane, isohexane, n-heptane,C8, C9 isoparaffins and mixtures thereof.

In one embodiment, the polymerisation is carried out in the presence ofhydrogen. Hydrogen is typically employed to help control polymerproperties, such as polymer molecular weight. In an alternativeembodiment, hydrogen is not added in step i. The skilled worker willappreciate, however, that hydrogen may be generated during thepolymerisation process. Thus, the hydrogen present in the polymerisationreaction mixture formed in step i. of the process may originate fromhydrogen which has been added as a reactant and/or hydrogen produced asa side product during polymerisation.

It will be appreciated that the propylene polymers may contain standardpolymer additives. These typically form less than 5.0 wt %, such as lessthan 2.0 wt % of the polymer material. Additives, such as antioxidants,phosphites, cling additives, pigments, colorants, fillers, anti-staticagent, processing aids, clarifiers and the like may thus be added duringthe polymerisation process. These additives are well known in theindustry and their use will be familiar to the artisan. Any additiveswhich are present may be added as an isolated raw material or in amixture with a carrier polymer, i.e. in so called master batch.

In one embodiment of the invention, the process for preparing themultimodal propylene butene copolymer may further comprise a step ofvisbreaking. The term “visbreaking” will be well known to the personskilled in the art and relates to a process which results in acontrolled breakdown of polymer chains, leading to rheological changes,typically an increase in MFR₂. Thus, the multimodal polymers of theinvention may be subject to visbreaking to finely tune their rheologicalprofile, as desired. Visbreaking may take place by several methods, asare well known in the art, such as thermal pyrolysis, exposure toionising radiation or oxidising agents. In the context of the presentinvention, visbreaking is typically carried out using peroxides.

Applications

Still further, the present invention relates to an article, preferably afilm, comprising the multimodal propylene butene random copolymer asdescribed above and to the use of such a multimodal propylene butenerandom copolymer for the production of an article, preferably a film.The films may be prepared by any known method in the art, such ascasting or extrusion.

The films of the invention may be multilayer or monolayer films, but arepreferably mono layer films. Moreover, the films of the inventionpreferably consist of the multimodal propylene butene copolymer of theinvention as the sole polymer component. However, it is to be understoodherein that the films may comprise further components such as additiveswhich may optionally be added in a mixture with a carrier polymer, i.e.in so called master batch.

Films of the invention which comprise (e.g. consist of) the multimodalpropylene butene random copolymer have a seal initiation temperature(SIT) (determined on 50 μm cast film as described in the experimentalpart) of 130° C. or less, such as 125° C. or less, more preferably 120°C. or less, more preferably of 118° C. or less. Whilst the SIT isideally as low as possible, typical lower limits might be 100° C., suchas 105° C.

Furthermore such films comprising the inventive copolymer shallpreferably have a tensile modulus determined according to ISO 527 at 23°C. on cast films with a thickness of 50 μm in machine direction as wellas in transverse direction of at least 490 MPa, more preferably at least500 MPa. Typically, the copolymer has a tensile modulus of less than 900MPa, such as less than 800 MPa.

The article, preferably film, of the invention may be employed in anumber of end applications, in particular food packaging applications.The articles of the current invention are especially suitable forcontaining food, especially frozen food, such as ice-cream, frozenliquids, sauces, pre-cooked convenience products, and the like.

It will be appreciated that any parameter mentioned above is measuredaccording to the detailed test given below. In any parameter where anarrower and broader embodiment are disclosed, those embodiments aredisclosed in connection with the narrower and broader embodiments ofother parameters.

The invention will now be described with reference to the followingnon-limiting examples.

Test Methods: Melt Flow Rate

The melt flow rate (MFR) is determined according to ISO 1133 and isindicated in g/10 min. The MFR is an indication of the melt viscosity ofthe polymer. The MFR is determined at 190° C. for PE and 230° C. for PP.The load under which the melt flow rate is determined is usuallyindicated as a subscript, for instance MFR₂ is measured under 2.16 kgload (condition D).

Density

Density of the polymer was measured according to ISO 1183/1872-2B.For the purpose of this invention the density of the blend can becalculated from the densities of the components according to:

$\rho_{b} = {\sum\limits_{i}{w_{i} \cdot \rho_{i}}}$

where ρ_(b) is the density of the blend,

-   -   w_(i) is the weight fraction of component “i” in the blend and    -   ρ_(i) is the density of the component “i”.

Quantification of Microstructure by NMR Spectroscopy

Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used toquantify the comonomer content of the polymers.Quantitative ¹³C{¹H} NMR spectra recorded in the molten-state using aBruker Avance III 500 NMR spectrometer operating at 500.13 and 125.76MHz for ¹H and ¹³C respectively. All spectra were recorded using a ¹³Coptimised 7 mm magic-angle spinning (MAS) probe head at 180° C. usingnitrogen gas for all pneumatics. Approximately 200 mg of material waspacked into a 7 mm outer diameter zirconia MAS rotor and spun at 4 kHz.This setup was chosen primarily for the high sensitivity needed forrapid identification and accurate quantification {klimke06, parkinson07,castignolles09} Standard single-pulse excitation was employed utilisingthe NOE at short recycle delays {klimke06, pollard04} and the RS-HEPTdecoupling scheme. {fillip05, griffin07} A total of 1024 (1 k)transients were acquired per spectra using a 3 s recycle delay.Quantitative ¹³C{¹H} NMR spectra were processed, integrated and relevantquantitative properties determined from the integrals. All chemicalshifts are internally referenced to the methyl isotactic pentad (mmmm)at 21.85 ppm {randall89}.Basic comonomer content method spectral analysis method:Characteristic signals corresponding to the incorporation of 1-butenewere observed {randall89} and the comonomer content quantified in thefollowing way.The amount of 1-butene incorporated in PPBPP isolated sequences wasquantified using the integral of the αB2 sites at 43.6 ppm accountingfor the number of reporting sites per comonomer:

B=I _(α)/2

The amount of 1-butene incorporated in PPBBPP double consecutivelysequences was quantified using the integral of the ααB2B2 site at 40.5ppm accounting for the number of reporting sites per comonomer:

BB=2*I _(αα)

When double consecutive incorporation was observed the amount of1-butene incorporated in PPBPP isolated sequences needed to becompensated due to the overlap of the signals αB2 and αB2B2 at 43.9 ppm:

B=(I _(α)−2*I _(αα))/2

The total 1-butene content was calculated based on the sum of isolatedand consecutively incorporated 1-butene:

Btotal=B+BB

The amount of propene was quantified based on the main Sαα methylenesites at 46.7 ppm and compensating for the relative amount of αB2 andαB2B2 methylene unit of propene not accounted for (note B and BB countnumber of butene monomers per sequence not the number of sequences):

Ptotal=I _(Sαα) +B+BB/2

The total mole fraction of 1-butene in the polymer was then calculatedas:

fB=Btotal/(Btotal+Ptotal)

The full integral equation for the mole fraction of 1-butene in thepolymer was:

fB=(((I _(α)−2*I _(αα))/2)+(2*I _(αα)))/(I _(Sαα)+((I _(Sα)−2*I_(αα))/2)+((2*I _(αα))/2))+((I _(α)−2*I _(αα))/2)+(2*I _(αα)))

This simplifies to:

fB=(I _(α)/2+I _(αα))/(I _(Sαα) +I _(α) +I _(αα))

The total incorporation of 1-butene in mole percent was calculated fromthe mole fraction in the usual manner:

B[mol %]=100*fB

The total incorporation of 1-butene in weight percent was calculatedfrom the mole fraction in the standard manner:

B[wt %]=100*(fB*56.11)/((fB*56.11)+((1−fβ)*42.08))

Details of these procedures can be found in Katja Klimke, MatthewParkinson, Christian Piel, Walter Kaminsky Hans Wolfgang Spiess, ManfredWilhelm, Macromol. Chem. Phys. 2006, 207, 382; Matthew Parkinson, KatjaKlimke, Hans Wolfgang Spiess, Manfred Wilhelm, Macromol. Chem. Phys.2007, 208, 2128; Patrice Castignolles, Robert Graf, Matthew Parkinson,Manfred Wilhelm, Marianne Gaborieau, Polymer 2009, 50, 2373; M. Pollard,K. Klimke, R. Graf, H. W. Spiess, M. Wilhelm, O. Sperber, C. Piel, W.Kaminsky, Macromolecules 2004, 37, 813; Xenia Filip, Carmen Tripon,Claudiu Filip, J. Magn. Reson. 2005, 176, 239; John M. Griffin, CarmenTripon, Ago Samoson, Claudiu Filip, Steven P. Brown, Mag. Res. in Chem.2007, 45(S1), S198; J. Randall Rev. Macromol. Chem. Phys. 1989, C29,201.

Molecular Weight & Molecular Weight Distribution

Molecular weight averages, molecular weight distribution (Mn, Mw,Mz MWD)Molecular weight averages (Mz, Mw and Mn), Molecular weight distribution(MWD) and its broadness, described by polydispersity index, PDI=Mw/Mn(wherein Mn is the number average molecular weight and Mw is the weightaverage molecular weight) were determined by Gel PermeationChromatography (GPC) according to ISO 16014-1:2003, ISO 16014-2:2003,ISO 16014-4:2003 and ASTM D 6474-12 using the following formulas:

$\begin{matrix}{M_{n} = \frac{\sum_{i = 1}^{N}A_{i}}{\sum_{i = 1}^{N}\left( {A_{i}/M_{i}} \right)}} & (1) \\{M_{w} = \frac{\sum_{i = 1}^{N}\left( {A_{i} \times M_{i}} \right)}{\sum_{i = 1}^{N}A_{i}}} & (2) \\{M_{z} = \frac{\sum_{i = 1}^{N}\left( {A_{i} \times M_{i}^{2}} \right)}{\sum_{i = 1}^{N}\left( {A_{i}/M_{i}} \right)}} & (3)\end{matrix}$

For a constant elution volume interval ΔV_(i), where A_(i), and M_(i)are the chromatographic peak slice area and polyolefin molecular weight(MW), respectively associated with the elution volume, V_(i), where N isequal to the number of data points obtained from the chromatogrambetween the integration limits.A high temperature GPC instrument, equipped with either infrared (IR)detector (IR4 or IR5 from PolymerChar (Valencia, Spain) or differentialrefractometer (RI) from Agilent Technologies, equipped with3×Agilent-PLgel Olexis and 1× Agilent-PLgel Olexis Guard columns wasused. As the solvent and mobile phase 1,2,4-trichlorobenzene (TCB)stabilized with 250 mg/L 2,6-Di tert butyl-4-methyl-phenol) was used.The chromatographic system was operated at 160° C. and at a constantflow rate of 1 mL/min. 200 μL of sample solution was injected peranalysis. Data collection was performed using either Agilent Cirrussoftware version 3.3 or PolymerChar GPC-IR control software.The column set was calibrated using universal calibration (according toISO 16014-2:2003) with 19 narrow MWD polystyrene (PS) standards in therange of 0.5 kg/mol to 11 500 kg/mol. The PS standards were dissolved atroom temperature over several hours. The conversion of the polystyrenepeak molecular weight to polyolefin molecular weights is accomplished byusing the Mark Houwink equation and the following Mark Houwinkconstants:

K _(PS)=19×10⁻³ mL/g,α_(PS)=0.655

K _(PE)=39×10⁻³ mL/g,α_(PE)=0.725

K _(PP)=19×10⁻³ mL/g,α_(PP)=0.725

A third order polynomial fit was used to fit the calibration data.

All samples were prepared in the concentration range of 0.5−1 mg/ml anddissolved at 160° C. for 2.5 hours for PP or 3 hours for PE undercontinuous gentle shaking.

Differential Scanning Calorimetry (DSC)

Differential scanning calorimetry (DSC) analysis, melting temperature(T_(m)) and melt enthalpy (H_(m)), crystallization temperature (T_(c)),and heat of crystallization (H_(c), H_(CR)) are measured with a TAInstrument Q200 differential scanning calorimetry (DSC) on 5 to 7 mgsamples. DSC is run according to ISO 11357/part 3/method C2 in aheat/cool/heat cycle with a scan rate of 10° C./min in the temperaturerange of −30 to +225° C. Crystallization temperature (T_(c)) and heat ofcrystallization (H_(c)) are determined from the cooling step, whilemelting temperature (T_(m)) and melt enthalpy (Hm) are determined fromthe second heating step.Throughout the patent the term Tc or (Tcr) is understood as Peaktemperature of crystallization as determined by DSC at a cooling rate of10 K/min.

Tensile Test on Films

Tensile tests according to ISO 527 at a temperature of 23° C. werecarried out on 10 mm wide strips cut in machine direction (MD) and intransverse direction (TD) from cast films of 50 μm thickness produced ona monolayer cast film line with a melt temperature of 220° C. and achill roll temperature of 20° C.

C6 FDA

It is measured based on FDA section 177.1520. 1 g of a polymer film of100 μm thickness is added to 400 ml hexane at 50° C. for 2 hours whilestirring with a reflux cooler. After 2 hours the mixture is immediatelyfiltered on a filter paper. The precipitate is collected in an aluminiumrecipient and the residual hexane is evaporated on a steam bath under N₂flow. The amount of hexane solubles is determined by the formula ((wt.sample+wt. crucible)−(wt crucible))/(wt. sample)×100%.

Dyna Test

The impact strength of films is determined by the Dynatest methodaccording to ISO7725-2 at 23° C. on cast films of 50 μm thicknessproduced on a monolayer cast film line with a melt temperature of 220°C. and a chill roll temperature of 20° C. with a thickness of 50 μm.The value Dyna/23° C. [J/mm] represents the relative total penetrationenergy per mm thickness that a film can absorb before it breaks dividedby the film thickness. The higher this value the tougher the material.

Haze

Haze was determined according to ASTM D1003-00 on cast films of 50 μmthickness produced on a monolayer cast film line with a melt temperatureof 220° C. and a chill roll temperature of 20° C.

Sterilisation

Steam sterilisation was performed in a Systec D series machine (SystecInc., USA). The samples were heated up at a heating rate of 5° C./minstarting from 23° C. After having been kept for 30 min at 121° C., theywere removed immediately from the steam steriliser and stored at roomtemperature until being processed further.

Xylene Soluble Fraction (XCS)

The amount of the polymersoluble in xylene is determined at 25° C.according to ISO 16152; 5th edition; 2005 Jul. 2001.

Flexural Modulus

The flexural modulus was determined in 3-point-bending at 23° C.according to ISO 178 on 80×10×4 mm³ test bars injection moulded in linewith EN ISO 1873-2.

Seal Initial Temperature (SIT)

The method determines the sealing temperature range (sealing range) ofpolypropylene films, in particular blown films or cast films accordingto ASTM F1921-12. Seal pressure, cool time and peel speed are modifiedas stated below. The sealing temperature range is the temperature range,in which the films can be sealed according to conditions given below.The lower limit (heat sealing initiation temperature (SIT)) is thesealing temperature at which a sealing strength of >5 N is achieved. Theupper limit (sealing end temperature (SET)) is reached, when the filmsstick to the sealing device.The sealing range is determined on a J&B Universal Sealing Machine Type3000 with a blown film of 50 μm thickness with the following furtherparameters:Specimen width: 25.4 mm

Seal Pressure: 0.1 N/mm² Seal Time: 0.1 sec

Cool time: 99 secPeel Speed: 10 mm/secStart temperature: 50° C.End temperature: 150° C.

Increments: 10° C.

specimen is sealed A to A at each sealbar temperature and seal strength(force) is determined at each step.

The temperature is determined at which the seal strength reaches 5 N.

EXPERIMENTAL Catalyst:

The catalyst used in the polymerisation processes for the C3C4 randomcopolymer composition of the inventive example (IE1) was prepared asfollows: The metallocene (MC1)(rac-anti-dimethylsilandiyl(2-methyl-4-phenyl-5-methoxy-6-tert-butyl-indenyl)(2-methyl-4-(4-tert-butylphenyl)indenyl)zirconiumdichloride) has been synthesized as described in WO 2013/007650.The catalyst was prepared using metallocene MC1 and a catalyst system ofMAO and trityl tetrakis(pentafluorophenyl)borate according to Catalyst 3of WO 2015/11135 with the proviso that the surfactant is2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoropropoxy)-1-propanol.

Production of the Multimodal Propylene Butene Random Copolymers of theInvention (IE1 and IE2)

The inventive examples (IE1 & IE2) were prepared in a two stagepolymerisation process, under the conditions outlined in Table 1, usinga catalyst as defined above. MFR of the final polymer was adjusted usingvisbreaking to the values shown in the Table. Properties of the variousfractions and final multimodal copolymers are also presented in Table 1.Film properties are shown in Table 3.

TABLE 1 Production Data for Inventive multimodal propylene butene randomcopolymers Unit IE1 IE2 Prepolymeriser Temperature ° C. 20 20 Residencetime min 20 20 Loop reactor Temperature ° C. 75 75 Feed H2/C3 ratiomol/kmol 0.1 0.1 Feed C4/C3 ratio mol/kmol 29.9 30.2 Split wt % 39 38MFR₂ g/10 min 2.0 2.0 C4 content wt % 5.5 5.5 First GPR Temperature ° C.80 80 H2/C3 ratio mol/kmol 1.1 1.1 C4/C3 ratio mol/kmol 60 107 Split wt% 61 62 MFR₂ g/10 min 2.0 1.9 C4 content after GPR wt % 7.0 10.3 PelletDensity C4 total wt % 6.6 9.1 MFR₂ g/10 min 9 10 Tm ° C. 138 138 XCS wt% 0.86 4.3 C6 FDA wt % 0.63 0.75 Flexural modulus MPa 1015 838The pelletization was done on a ZSK 32 twin screw extruder. The desiredamount of PP powder, additives (1000 ppm of B215 supplied by BASF, 500ppm of calcium stearate from Baerlocher) and proper amount of Triganox101 (AkzoNobel) were mixed and extruder at 220° C., with a throughput of100 kg/h. The amount of Triganox 101 was adjusted by man skilled in theart to reach the target final MFR. The properties measured on thepellets are reported in Table 1.

Production of Comparative Copolymers (CE1 & CE2)

CE1 is a single site catalyzed unimodal propylene butene randomcopolymer prepared using the catalyst described above, C4 content 6.1 wt% and MFR₂ after visbreaking 12 g/10 min. CE2 is a Ziegler-Nattacatalyzed propylene ethylene random copolymer, MFR₂ 8 g/10 min.

Preparation of the Ziegler-Natta Catalyst for CE2: Used Chemicals:

20% solution in toluene of butyl ethyl magnesium (Mg(Bu)(Et), BEM),provided by Chemtura2-ethylhexanol, provided by Amphochem3-Butoxy-2-propanol—(DOWANOL™ PnB), provided by Dowbis(2-ethylhexyl)citraconate, provided by SynphaBaseTiCl4, provided by Millenium ChemicalsToluene, provided by AspokemViscoplex® 1-254, provided by EvonikHeptane, provided by Chevron

Preparation of a Mg Alkoxy Compound:

Mg alkoxide solution was prepared by adding, with stirring (70 rpm),into 11 kg of a 20 wt % solution in toluene of butyl ethyl magnesium(Mg(Bu)(Et)), a mixture of 4.7 kg of 2-ethylhexanol and 1.2 kg ofbutoxypropanol in a 20 l stainless steel reactor. During the additionthe reactor contents were maintained below 45° C. After addition wascompleted, mixing (70 rpm) of the reaction mixture was continued at 60°C. for 30 minutes. After cooling to room temperature 2.3 kg g of thedonor bis(2-ethylhexyl)citraconate was added to the Mg-alkoxide solutionkeeping temperature below 25° C. Mixing was continued for 15 minutesunder stirring (70 rpm).

Preparation of Solid Catalyst Component:

20.3 kg of TiCl4 and 1.1 kg of toluene were added into a 20 l stainlesssteel reactor. Under 350 rpm mixing and keeping the temperature at 0°C., 14.5 kg of the Mg alkoxy compound prepared in example 1 was addedduring 1.5 hours. 1.7 l of Viscoplex® 1-254 and 7.5 kg of heptane wereadded and after 1 hour mixing at 0° C. the temperature of the formedemulsion was raised to 90° C. within 1 hour. After 30 minutes mixing wasstopped catalyst droplets were solidified and the formed catalystparticles were allowed to settle. After settling (1 hour), thesupernatant liquid was siphoned away. Then the catalyst particles werewashed with 45 kg of toluene at 90° C. for 20 minutes followed by twoheptane washes (30 kg, 15 min). During the first heptane wash thetemperature was decreased to 50° C. and during the second wash to roomtemperature.The thus obtained catalyst was used along with triethyl-aluminium (TEAL)as co-catalyst and dicyclopentyl dimethoxy silane (D-Donor) as donor forpreparing the polymer CE2The pelletization was done on a ZSK 32 twin screw extruder. The desiredamount of PP powder, additives (1000 ppm of B215 supplied by BASF, 500ppm of calcium stearate from Baerlocher) and proper amount of Triganox101 (AkzoNobel) were mixed and extruder at 220° C., with a throughput of100 kg/h. The amount of Triganox 101 was adjusted by man skilled in theart to reach the target final MFR. The properties measured on thepellets are reported in Table 2. Film properties are shown in Table 3.

TABLE 2 Production Data for Comparative copolymers Unit CE1 CE2Prepolymeriser Temperature ° C. 20 29 Residence time Min 20 20 LoopTemperature ° C. 70 70 Pressure Bar 55 55 Feed H2/C3 mol/kmol 0.1 0.6Feed C2/C3 mol/kmol 0 7.5 Feed C4/C3 mol/kmol 33 0 MFR g/10 min 1.7 1.8C2 wt % 0 3.5 C4 wt % 6.1 0 split wt % 100 41 First GPR Temperature ° C.Not in use 80 H2/C3 mol/kmol 58 C2/C3 mol/kmol 27 MFR g/10 min 1.7 C2 wt% 4.1 Pellets C2 total wt % 0 4.1 C4 total wt % 6.1 0 MFR g/10 min 12 8Tm ° C. 139 140 C6 FDA wt % 1.16 2.5 XCS wt % 1.55 9.8 Flexural modulusMPa 1089 850

Film Production

Films were produced on a Collin 30 lab scale cast film line, with a melttemperature of 220° C. and chill roll temperature of 20° C. thethroughput was 8 kg/h. The film thickness is 50 μm.

TABLE 3 Film properties for Inventive and Comparative multimodalpropylene copolymers IE1 IE2 CE1 CE2 TM/MD MPa 616 514 599 488 TM/TD MPa594 508 573 501 Dyna/23° C. J/mm 16.6 17.8 17.5 37.5 Haze/b.s. % 0.340.55 0.38 0.17 Haze/a.s. % 0.26 1.39 0.61 15 SIT ° C. 112 107 113 114

1. A multimodal propylene butene random copolymer having a melt flowrate (MFR₂) of 1.0 to 20.0 g/10 min and a butene content of 5.0 to 20.0wt %, wherein said copolymer is prepared using a single site catalystand wherein said copolymer comprises: (i) 30 to 70 wt % of a propylenebutene copolymer (A) having an MFR₂ of 0.5 to 20.0 g/10 min and a butenecontent of 2.0 to 10.0 wt %; and (ii) 70 to 30 wt % of a propylenebutene copolymer (B) having an MFR₂ of 0.5 to 20.0 g/10 min and a butenecontent of 4.0 to 20.0 wt %; wherein copolymers (A) and (B) aredifferent.
 2. The multimodal propylene butene random copolymer asclaimed in claim 1, wherein said single site catalyst is a metallocenecatalyst.
 3. The multimodal propylene butene random copolymer as claimedin claim 1, wherein the butene content of said multimodal copolymer isin the range 6.0 to 16.0 wt %.
 4. The multimodal propylene butene randomcopolymer as claimed in claim 1, wherein a xylene soluble fraction isless than 10.0 wt %.
 5. The multimodal propylene butene random copolymeras claimed in claim 1, wherein said copolymer is substantially free ofethylene.
 6. The multimodal propylene butene random copolymer as claimedin claim 1, wherein said copolymer has a flexural modulus of at least750 MPa.
 7. The multimodal propylene butene random copolymer as claimedin claim 1, wherein said copolymer has a molecular weight distribution(Mw/Mn) of less than 4.5.
 8. The multimodal propylene butene randomcopolymer as claimed in claim 1, wherein the MFR₂ of the copolymer is inthe range 4.0 to 12.0 g/10 min.
 9. A process for the preparation of themultimodal propylene butene random copolymer as defined in claim 1, saidprocess comprising: (i) polymerising propylene and butene in a firstpolymerisation stage in the presence of a single site catalyst toprepare a first propylene butene copolymer having a MFR₂ from 0.5 to20.0 g/10 min and a butene content of 2.0 to 10.0 wt %; (ii)polymerising propylene and butene in a second polymerisation stage inthe presence of said catalyst and said first propylene butene copolymerto prepare said multimodal propylene butene copolymer.
 10. The processas claimed in claim 9, wherein the first polymerisation stage is carriedout in a loop reactor and the second polymerisation stage is carried outin a gas phase reactor.
 11. An article comprising the multimodalpropylene butene copolymer as defined in claim
 1. 12. The article asclaimed in claim 11, wherein said article is a film.
 13. (canceled) 14.The article of claim 12, wherein the film is a monolayer film.
 15. Aprocess of making an article comprising the multimodal propylene butenecopolymer as defined in claim 1.